In his important paper “1953 and All That: A Tale of Two Sciences” (1984), Philip Kitcher defends biological antireductionism, arguing that the division of biology into subfields such as classical and molecular genetics is “not simply … a temporary feature of our science stemming from our cognitive imperfections but [is] the reflection of levels of organization in nature” (p. 371). In a recent discussion of Kitcher's views, Alexander Rosenberg has argued, first, that Kitcher has shown that the reduction of classical to molecular genetics is impossible only because of our intellectual limitations and, second, that this kind of antireductionism supports an instrumentalist approach to biological theory. I argue that both of Rosenberg's claims should be rejected despite the fact that Kitcher misdiagnoses the central reason for the failure of reduction.

A few years ago, Bas van Fraassen reminded philosophers of science that there are two central questions that a theory of explanation ought to answer. First, what is a (good) explanation—when has something been explained satisfactorily? Second, why do we value explanations? (van Fraassen, 1977, 1980, ch. 5). For a long time, discussions of explanation concentrated on technical problems connected with the first of these questions, and the second was by and large ignored. But, in fact, I think it is the second question which raises the more fundamental and interesting philosophical issues. I shall offer reasons for thinking that the answer to the first question requires acceptance of the sort of fullblown notion of causation that only a scientific realist can love, and that the answer to the second question requires a realist construal of scientific theories and scientific methodology. My argument will be mainly negative, surveying the problems facing some major alternative accounts of explanation. A full elaboration of the realist perspective will have to await the completion of work in progress.